ANATOMY OF A CHELONIAN. 



movable and less opaque than the eyelids 

 proper. 

 /. Just behind the angle of the gape, the tym- 

 panic membrane will be seen as a circular 

 slightly depressed area of skin, around the 

 margin of which a hard supporting ring can 

 be felt. 



4. The Interior of the Month Cavity. 



a. Open the mouth and observe that the horny 

 plates covering the jaws extend in for some 

 way over both floor and roof of the buccal 

 cavity ; also that each has a second notched 

 ridge within the one forming its outer boun- 

 dary. Into the groove between the two up- 

 per ridges the external lower ridge fits, and 

 similarly the inner ridge of the upper jaw fits 

 between the two ridges of the lower. 



b. On the roof of the mouth, note that the horny 

 plate is succeeded by diverging folds of mu- 

 cous membrane, between which are seen the 

 openings of the posterior nares with the back 

 edge of the septum narium between them. Note 

 also that the eyeballs do not cause projections 

 on the roof of the mouth, as in the frog, but 

 are completely separated from it by a hard 

 partition. 



c. On the floor of the mouth is seen the short, con- 

 ical, pointed, and but slightly movable tongue. 

 At the base of the tongue is a considerable 

 elevation, in which is the longitudinal slit of 

 the aditus laryngis, unprotected by an epi- 

 glottis. 



